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EXTENDING FLUPROPANATE USE – SPOT APPLICATION ON PERENNIAL MISSION
AND GAMBA GRASS
Wayne Vogler, Emma Carlos and Kelsey Hosking
Biosecurity Queensland, Department of Agriculture and Fisheries, Tropical Weeds
Research Centre, P.O Box 187 Charters Towers, Queensland 4820, Australia.
ABSTRACT
Perennial mission grass (Cenchrus polystachios) and gamba grass (Andropogon gayanus)
are two highly invasive grasses present in north Queensland. Currently, herbicide control
options for these species are limited to non-selective herbicides such as glyphosate that
result in significant off-target damage. In this study, field trials were conducted to investigate
the efficacy of spot applications of flupropanate (liquid and granular) into the tussock as a
selective herbicide option for these grasses. Australian Pesticides and Veterinary Medicines
Authority (APVMA) approval will be sought for the use of: 4.5 g/tussock of GP Flupropanate
and 0.6 ml/tussock of Tussock™ for perennial mission grass control; and 9 g/tussock of GP
Flupropanate and 1.2 ml/tussock of Tussock™ for gamba grass control. These rates were
selected as the most efficacious, although efficacy was not significantly higher than lower
rates, it is expected that these rates will be more effective under marginal conditions. In
summary, spot application of flupropanate is an effective and practical method for controlling
these invasive grasses with particular application in areas such as revegetation sites, sites
in the early stages of invasion with limited or scattered infestations and sites where the
northern wet season can limit access for high-volume herbicide application.
Keywords: Flupropanate, perennial mission grass, gamba grass, spot application.
INTRODUCTION
Perennial mission grass (Cenchrus polystachios) and gamba grass (Andropogon gayanus)
are two highly invasive grasses present in north Queensland. Perennial mission grass
remains undeclared in Queensland though in the Northern Territory it is a Class B and Class
C weed under the Weeds Management Act 2001. Gamba grass is listed as category 3
restricted matter under the Biosecurity Act 2014 in Queensland and recognised as a Weed
of National Significance in Australia. Each of these grasses compete strongly with native
pasture and their high biomass can fuel intense bushfires that damage ecosystems and
threaten the safety of people and property (Department of Agriculture and Fisheries,
Biosecurity Queensland 2016, Northern Territory Government of Australia 2017). Despite
the significant negative impacts of these grasses, herbicide control options are limited. Most
registered herbicides are non-selective, such as glyphosate, and can cause non-target
damage, or mortality, to surrounding desirable species. This can reduce competition for
invasive species and leave areas open to further invasion. With this in mind, a selective
herbicide could greatly improve management of these invasive grasses. Flupropanate is a
selective, soil-active, residual herbicide that requires rainfall to enter the soil and be
absorbed through the root system of plants. A single application has the potential to control
mature plants and germinating seedlings, although effectiveness and timeframes will vary
depending on soil type and rainfall. The effect of flupropanate on perennial mission and
gamba grass is not known, although anecdotes suggest that it may be useful for their control.
This trial investigated whether individual perennial mission and gamba grass tussocks could
be effectively controlled with a single spot application of liquid or granular flupropanate.
METHODS
The herbicides Tussock™ (745 g/L flupropanate) and GP Flupropanate (86.9 g/kg
flupropanate) were used for all liquid and granular flupropanate treatments respectively. All
trials were established in October 2013 using a completely randomised block design.
Experimental units comprised 4 m x 4 m plots, with each treatment replicated four times.
Perennial mission grass
The trial site (16°57’53.42”S, 145°24’33.43”E°) was located within a grassy woodland where
patches of perennial mission grass had established. Plots contained an average of 15
perennial mission grass plants, with mean basal diameters of 15.8 cm. Tussock™ and GP
Flupropanate were tested at 0.3, 0.6 and 1.2 ml/tussock; and 2.25, 4.5 and 9.0 g/tussock
respectively for efficacy against a control (no flupropanate). The respective rates of each
formulation contained the same amount of active ingredient. Measured doses of Tussock™
and GP Flupropanate were applied to the centre of all tussocks in each plot. Tussock™
treatments were applied with a N.J. Phillips® 5 ml Tree Injector as a single 4 ml shot of
herbicide/water solution per tussock while GP Flupropanate treatments were hand applied.
Herbicide efficacy was assessed at 106 and 183 days after treatment (DAT) by rating each
tussock as alive or dead. Mortality (%) was analysed, and this was calculated as the number
of dead tussocks over the total number of treated tussocks. The impact of herbicide
treatments on adjacent non-target grasses and broadleaf plants was assessed by
measuring the distance (cm) between treated tussocks and the nearest non-target grass
and broadleaf plant that was alive. At 183 DAT, the total number of stems with emerged
seed heads was counted in each plot.
Gamba grass
The trial site (16°58’58.28”S, 145°15’49.53”E°) was located on cleared agricultural land
dominated by gamba grass. Plots contained an average of 30 gamba grass plants, with
mean basal diameters of 12.9 cm. Prior to the commencement of the trial, cattle had grazed
the site, making tussocks accessible and easily treated on an individual basis. Cattle were
excluded for the duration of the trial. Tussock™ and GP Flupropanate were tested using
the application rates and methodology used for perennial mission grass (see above).
Herbicide efficacy was assessed at 133 and 182 DAT by rating each tussock as alive or
dead. However, as there had been significant gamba grass recruitment, gamba grass
tussocks that were ≤5 cm in size were considered to have been recruited from seed since
treatment application and were not included in the efficacy assessments. Mortality (%) was
analysed, and this was calculated as the number of dead tussocks over the total number of
treated tussocks. At 182 DAT, the total number of gamba grass stems with emerged seed
heads was counted in each plot. Tussocks that were ≤5 cm were also counted in each plot
to assess lateral movement and residual effects of the herbicide on ‘new plants’.
Statistical analyses
Randomised complete block ANOVAs (p<0.05) were used to assess treatment effects.
Where required, data was transformed (log10 + 0.1) to meet ANOVA assumptions. Means
or back-transformation of the geometric means are presented. Treatment means were
separated according to Fisher’s Protected LSD (p<0.05).
RESULTS
Perennial mission grass
Mortality of perennial mission grass tussocks 106 DAT was significantly different between
treatments (p<0.001), with nil mortality in controls and the highest and middle herbicide rates
having similarly high mortality (Table 1). There was an increase in mortality over time and
by 183 DAT, mortality of tussocks remained significantly different between treatments
(p<0.001). While the highest GP Flupropanate treatment (9.0 g) resulted in the greatest
mortality of mission grass, at 183 DAT it was not significantly higher than any other herbicide
treatment, except the 2.25 g GP Flupropanate treatment. Stems with emerged seed heads
in the control plots averaged 22.6 at 183 DAT which was significantly higher than all
herbicide treatments (Table 1) (p<0.001). There was little impact on non-target species at
106 DAT with no significant difference (p>0.05) between the control and herbicide
treatments in the average distance from a treated tussock to the nearest live non-target
grass or broadleaf plant, which averaged 9.19 cm.
Table 1. Mean tussock mortality and number of stems with emerged seed heads per plot.
Means within columns followed by the same letter are not significantly different (p>0.05).
Gamba grass
There was a significant treatment effect on mortality of gamba grass tussocks 133 DAT
(p<0.05). In control plots, all initial plants remained alive, compared to the herbicide
treatments where >60% mortality was recorded (Table 2). The two highest rates of GP
Flupropanate had significantly higher tussock mortality than the lowest Tussock™ rate, while
tussock mortality was not significantly different between all other treatments (Table 2).
There was a significant difference in the number of new plants (<5 cm in size) between
treatments (p<0.05), with the Tussock™ treatments generally having fewer new plants
compared to the GP Flupropanate treatments and controls (Table Table 2). There was on
average 42.8 stems with emerged seed heads in the highest GP Flupropanate treatment at
182 DAT which was significantly fewer (p<0.05) than in all other treatments (Table 2).
Table 2. Mean tussock mortality, number of new plants and number of stems with emerged
seed heads per plot. Means or back transformations of geometric means (*) within columns
followed by the same letter are not significantly different (p<0.05).
Treatment
Rate
Tussock mortality
133 DAT (%)
Number of new plants
per plot 133 DAT
Number of stems with emerged
seed heads* per plot 182 DAT
Control
NA
0.0 a
8.3 b
215.0 a
Tussock™
0.3 ml
61.1 b
5.8 ab
164.3 a
Tussock™
0.6 ml
67.3 bc
1.3 a
107.5 a
Tussock™
1.2 ml
78.6 bc
6.5 ab
147.0 a
GP Flupropanate
2.25 g
83.0 bc
10.5 b
301.8 a
GP Flupropanate
4.5 g
88.7 c
9.8 b
280.8 a
GP Flupropanate
9.0 g
92.0 c
10.8 b
42.8 b
Treatment
Rate
Tussock mortality
106 DAT (%)
Tussock mortality
183 DAT (%)
Number of stems with emerged
seed heads per plot 183 DAT
Control
NA
0.0 d
13.6 c
22.6 a
Tussock™
0.3 ml
45.6 bc
83.9 ab
3.6 b
Tussock™
0.6 ml
77.7 a
90.9 a
0.9 b
Tussock™
1.2 ml
89.8 a
87.9 ab
1.0 b
GP Flupropanate
2.25 g
36.6 c
65.7 b
5.0 b
GP Flupropanate
4.5 g
68.5 ab
87.5 ab
0.9 b
GP Flupropanate
9.0 g
78.0 a
97.3 a
4.8 b
DISCUSSION
Spot application of at least one rate of each herbicide was effective for controlling perennial
mission and gamba grass tussocks, although gamba grass generally required higher rates
to achieve satisfactory mortality. Even then, mortality averaged less than 80% using
Tussock™ which is towards the lower range for acceptable herbicide efficacy. Lateral
movement of herbicides from treated tussocks appeared negligible, with no impact on
adjacent plants. Emergence of new gamba grass plants also suggested no residual impact
on areas surrounding tussocks. Follow up treatment will be essential to control emerging
seedlings.
While not practical on a large scale or for dense monocultures, spot application of
flupropanate products has a place in control of perennial mission and gamba grass. The
high-concentration low-volume method of applying Tussock™ provides a treatment option
for hard to access areas where using heavy spray equipment is impractical. GP
Flupropanate offers the opportunity to immediately treat tussocks encountered by chance
as its granular formulation is easily portable and does not require mixing or dilution. All
flupropanate products are soil-active and require rainfall to enter the soil and be absorbed
through the root system of plants. These products can be applied during the dry season
and become active in the wet season, allowing control when access to apply herbicides is
restricted by weather and road conditions.
Given its advantages, the potential to extend this method to other invasive grasses such as
African fountain (Cenchrus setaceus), giant rat’s tail (Sporobolus pyramidalis and S.
natalensis) and Guinea grass (Megathyrsus maximus var maximus) warrants investigation.
Spot application of flupropanate provides an effective and practical method for controlling
both perennial mission and gamba grass in areas such as revegetation sites, sites in the
early stages of invasion with limited or scattered infestations and sites where the northern
wet season can limit access for herbicide application. A minor use permit application will be
submitted to the Australian Pesticides and Veterinary Medicines Authority (APVMA) to
extend the control options available to land managers for these invasive grasses.
ACKNOWLEDGMENTS
The authors thank John Clarkson (Queensland Parks and Wildlife Service) and Sid Clayton
(Mareeba Shire Council) for their support. Thanks also to Shane Campbell and Joe Scanlan
for commenting on earlier versions of this paper. Funded by the Department of Agriculture
and Fisheries.
REFERENCES
Department of Agriculture and Fisheries, Biosecurity Queensland (2016) ‘Gamba grass,
Andropogon gayanus’. https://www.daf.qld.gov.au/__data/assets/pdf_file/0011/67466/IPA-
Gamba-Grass-PP147.pdf. (Queensland Government, Brisbane).
Northern Territory Government of Australia (2017) ‘Mission grass’.
https://nt.gov.au/environment/weeds/list-of-declared-weeds-in-the-nt/mission-grass.
(Northern Territory Government of Australia, Darwin).